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Head to the spring on the right, jump up and collect the balloon. Return to the balloon you bypassed and take it, and go through the door above you.

Jump up into the gap covered by the wooden beam and screw, and head down the left area, grabbing the balloon. Climb back up on the right until you reach the top. Jump, and smash your way down the bricks.

You should now appear at the top, perched on a screw. Charge downward, collecting the acorns as they appear on the map. Get the baloon and head through the doorway.

Continue to the right. The first set of floor traps will only rise upward when you are above them. Go to the right via the top path, and head slightly back to activate the circle switch. Continue to the right; these floor traps will self-destruct, shooting two bullets when they reach your level; jump to avoid them. Collect the balloon, and activate the star switch while deactivating the circle switch.

Head to the top left to enter the final section. If you didn't disable the circle switch or enable the star switch, you will have to redo the previous section.

In the final section, head downward to collect the last balloon. You will need to work your way through the patrolling snails, but the path is not otherwise difficult.

[edit] Secrets

In the final section, you can reach the 1up by jumping up and walking over the top of the map. Otherwise, head downward to collect the last balloon.

The watering can is located at the top of the vertical area. To reach it, bypass the balloon at the bottom and return later once you took all other balloons. You have a final chance to collect acorns on the way up before collecting the watering can on the left.